1. Field of the Invention
The present invention generally relates to a bidirectional communication system through a node handling HTTP (HyperText Transfer Protocol) traffic, and in particular to a bidirectional communication system having a HTTP tunneling function to allow real-time information sharing among a plurality of users such as groupware users.
2. Description of the Related Art
Real-time information sharing on the Internet can be achieved by using a dedicated protocol to connect between a server and a plurality of clients. For example, when a change to shared information is made at a client, the change is promptly transferred to the server.
In the case of connecting a so-called Intranet to the Internet, security is one of the most important concerns. A common method for ensuring security is to install a firewall or a proxy server, which is a secure single point of attachment to the Internet. In many cases, a firewall host allows only HTTP traffic to pass through as specified by the firewall administrator.
In such a system using a firewall as a secure single point of attachment to the Internet, it is necessary to devise a method of passing through the firewall while ensuring security. In general, a HTTP protocol converting method of converting transmission data into HTTP traffic is employed. The reason is that almost all firewalls are provided with an HTTP proxy and therefore there is no need of changing the existing system software or configuration.
An a conventional example, a lightweight secure tunneling protocol or LSTP has been proposed in Japanese Patent Application Unexamined Publication No. 10-285216 corresponding to U.S. Pat. No. 6,104,716. The LSTP permits communicating across one or more firewalls by using a middle server or proxy.
However, HTTP is a communications protocol such that an interaction between a server and a client in completed in a single transaction. More specifically, when receiving a request, the server in permitted only to transmit HTML (HyperText Makeup Language) pages to the client that has originated the request. Therefore, in the case of a real-time information sharing system employing the HTTP protocol converting method, all the clients periodically transmit an information update request to the server so as to share the same information among the clients. A typical example is “Chat” in an electronic conference system using an HTML browser.
As described above, an information update request is periodically transmitted to the server in the case of no information update, resulting in increased needless traffic in the network and increased communication charge.
Further, since only a client originates the information update request, sufficient real-time information update cannot be achieved.
There has been “RealAudio” system, as another conventional example, which supports live and on-demand audio over the Internet by keeping an HTTP transaction to allow long time data stream. However, the RealAudio system provides only one-directional communication. Therefore, it cannot be applied to a bidirectional communication system.